Wafers are known to be made of a semiconductor material, such as silicon. The SMART-CUT® process, for instance, is known for annealing and detaching a layer from such a wafer at a zone of weakness, is an example of a process implementing such stages. The surface of layers produced are desired to satisfy very strict specifications. It is common to find roughness specifications that must not exceed 5 Angstroms in terms of rms (root mean square).
Measurements of roughness are generally taken with an AFM (Atomic Force Microscope). With this type of device, the roughness is measured on surfaces scanned by the tip of the AFM, ranging from 1×1 μm2 to 10×10 μm2, and less commonly to 50×50 μm2 or even 100×100 μm2.
It is also possible to measure the surface roughness by other methods, such as via a “haze”. This method notably has the advantage of quickly characterising the harmony of the roughness over a whole surface. The haze, which is measured in ppm, comes from a process using the optical reflective properties of the surface to be characterized, and corresponds to an optical “background noise” diffused by the surface due to its micro-roughness.
It is also to be noted that if the layers are to have certain roughness values, they should also have a harmonious roughness over their whole surface.
The processes known in the art that allow the detachment of a layer from a wafer of semiconductor material following an annealing do not always result in layer surface roughness that falls within the aforementioned specifications. There is thus a need to improve the controlling of the roughness of detached layers following an annealing.